24.两两交换链表中的节点

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class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if(!head)
            return nullptr;
        return helper(head, head->next);
    }
    ListNode* helper(ListNode* head, ListNode* head2) {
        if(!head || !head2)
            return head;
        head->next = head2->next;
        head2->next = head;
        head->next = helper(head->next, head->next ? head->next->next : nullptr);
        return head2;
    }
};

Accepted

55/55 cases passed (4 ms)

Your runtime beats 83.69 % of cpp submissions

Your memory usage beats 19.24 % of cpp submissions (8.7 MB)